Helen Jewell at Reuters made a point this week that I've been preaching for longer than some of you have been investing: the hunt for actual diversification isn't dead, it's just misunderstood. Her piece on equity diversification hits on something I think a lot of investors are quietly worrying about right now.

The concern is straightforward. Tech has gotten so dominant in the major indexes that owning an S&P 500 fund feels less like owning 500 companies and more like owning a handful of names with 494 smaller ones along for the ride. When the top five or six stocks make up a quarter of the index, your "diversified" portfolio has a pretty serious concentration problem hiding inside it.

I lived through the late 1990s. This feels familiar. Different sector, same energy. Everyone piles into whatever is working, the weightings get top-heavy, and then gravity shows up uninvited.

Jewell's argument is that real diversifiers are still out there in plain sight. International stocks, small caps, certain sectors that don't march in lockstep with the megacap tech trade. The boring stuff, basically. The things that make you yawn when you look at the returns in a given quarter but keep you from getting shredded when the momentum trade finally rolls over.

And diversification means holding things that are underperforming. That is literally what it does. If everything in your portfolio is going up at the same time, you are not diversified, you are leveraged to the same bet. You just do not know it yet.

I've been adding to international funds for about two years now. Not because I think US stocks are done. I don't. But because the gap between US and international performance over the past decade is historically wide, and those gaps have a way of closing eventually. Maybe not this year. Maybe not next. But over a retirement timeline, mean reversion is one of the few things you can reasonably count on.

Small caps are another one. They've been left for dead while everyone chases the big names. Fine by me. I've been dollar-cost averaging into a small-cap index fund and will keep doing it whether the news is good or bad.

The temptation right now is to just buy the popular stuff and call it a day. I understand that pull. When something is working, why fight it? But markets have a cruel habit of punishing the crowd at exactly the wrong moment. The people who were "diversified" into four different tech funds in early 2000 learned that lesson the hard way.

When was the last time you actually looked at what's inside your index funds?

The answer, for most people, is never. And that's okay as a starting point. But at some point you owe it to yourself to peek under the hood and ask whether you're as spread out as you think you are. Sometimes the best diversifiers are the ones nobody's talking about.